Pressurized gas blast type electrical switch having blast valve removable for servicing without loss of gas

ABSTRACT

An electrical switch of the type which utilizes a pressurized gas such as SF6 working in a closed system for blasting the switch contacts with the gas in order to facilitate extinction of the arc includes high and low pressure gas tanks, the gas being stored in the high pressure tank and being delivered through a gas blast valve to a housing enclosing the switch contacts and which is located in the low-pressure tank. The gas after blasting the switch contacts flows from the switch contact housing into the low pressure tank. To facilitate servicing of the gas blast valve without loss of gas from either the high or low pressure tanks, the interior of the blast valve including the movable parts and seals is made accessible from the exterior of the tanks and provision is made for sealing off the two tanks from the interior of the blast valve.

United States Patent [72] Inventor Dieter F loessel Fislisbach, Switzerland [21] App1. No. 841,701

[22] Filed July 15, 1969 [45] Patented July 27, 1971 73] Assignee Aktiengesellschaft Brown Boveri & Cie Baden, Switzerland [32] Priority July 30, 1968 [33] Switzerland (54] PRESSURIZED GAS BLAST TYPE ELECTRICAL SWITCH HAVING BLAST VALVE REMOVABLE FOR SERVICING WITHOUT LOSS OF GAS Primary Examiner-Robert S. Macon Attorney-Pierce, Scheffler & Parker ABSTRACT: An electrical switch of the type which utilizes a pressurized gas such as SF6 working in a closed system for blasting the switch contacts with the gas in order to facilitate extinction of the arc includes high and low pressure gas tanks, the gas being stored in the high pressure tank and being delivered through a gas blast valve to a housing enclosing the switch contacts and which is located in the low-pressure tank. The gas after blasting the switch contacts flows from the switch contact housing into the low pressure tank. To facilitate servicing of the gas blast valve without loss of gas from either the high or low pressure tanks, the interior of the blast valve including the movable parts and seals is made acccssiblefrom the exterior of the tanks and provision is made for sealing off the two tanks from the interior of the blast valve.

PRESSURIZED GAS BLAST TYPE ELECTRICAL SWITCH HAVING BLAST VALVE REMOVABLE FOR SERVICING WITHOUT LOSS OF GAS The present invention relates to an improvement in electrical switches of the type in which a relatively expensive pressurized gas such as SF6 is utilized for blasting the contacts as they open in order to facilitate arc extinction, the gas circuit for the switch being operated on a closed cycle in which the gas, after purification, is stored in a high-pressure tank for reuse, as distinguished from open-cycle operation wherein the gas used for blasting the contacts is simply discharged into the atmosphere.

More particularly, the invention relates to an electrical switch of the class described and has for an object the improvement wherein a blast valve controlling flow of the pressurized gas from the high-pressure storage tank to the switch contacts and thence into a low-pressure tank is so arranged that the interior of the blast valve structure is readily accessible for taking apart for purposes of periodic inspection and replacement of parts subject to wear such as valve seals and the like. Moreover, due to the novel arrangement of the blast valve structure, the gas passageways which extend through the valve from the high-pressure storage tank to the switch contacts and thence to the low-pressure tank can be effectively sealed off so that there is no loss of the relatively valuable gas to the exterior while the blast valve is being serviced.

With the known types of gas blast switches operating on a closed cycle, the switch contacts are located in a low-pressure chamber which is designed as a grounded metal tank, the tank being filled with insulating gas at relatively low pressure, for example SF6 at 3 atmospheres. For arc extinction, the same gas is fed from a high-pressure tank at a pressure of, for example, l4 atmospheres located within the low-pressure tank. With such an arrangement, the blast valve controlling the gas flow is thus relatively inaccessible and can be inspected only when the switch structure is opened after the pressure gas has been discharged from both the high and low pressure tanks. In the case of gases such as SF6, the discharge and subsequent refilling of the tanks is thus a costly and time consuming procedure which thus as a practical matter limits inspections to those wherein a replacement of switch contacts would normally be involved. Since the switch contacts are normally designed so as to have a useful life of several years, this means that successive inspections can be scheduled at intervals of several years. However, the blast valve structure which includes seals both of the sliding and pressure type is not so durable since the seals are obviously subject to wear and hence require inspection and replacement at much shorter intervals. The present invention, which thus renders the blast valve structure readily accessible from the exterior of the overall switch structure for disassembly and parts replacement without suffering a loss of pressure gas is thus believed to constitute a substantial improvement over the known switch organization of this general type.

The foregoing objects and other advantages inherent in the invention will become more apparent from the following detailed description of two embodiments thereof and from the accompanying drawings illustrating the same wherein:

FIG. 1 is a view partly in central vertical section and partly in elevation illustrating the arrangement of the high and low pressure gas tanks, with the switch contacts being located within an insulating chamber in the low-pressure tank and with the blast valve being located partially within the highpressure tank and with its upper end protruding through the tank wall so as to provide ready access to the interior thereof;

FIG. 2 is a view in central vertical section, drawn to an enlarged scale, of the blast valve depicted in FIG. I, the valve being shown in its closed position blocking gas flow from the high-pressure tank to the switch contacts;

FIG. 3 is a vertical half-section of the valve structure illustrated in FIG. 2 but with the valve in open position in which gas is passed from the high pressure tank through the valving to the switch contacts;

FIG. 4 is also a vertical half-section of the valve with its internal structure displaced to a position sealing off the gas outlet ports from the high-pressure tank and also sealing off the gas inlet to the switch contact chamber preliminary to dismantling the valve structure for inspection and parts replacement;

FIG. 5 is a vertical half-section similar to FIG. 4 after those parts of the valve which include the slidable seals have been removed; and

FIG. 6 is a view in central vertical section of a modified construction for the blast valve according to the invention.

With reference now to the drawings and to FIG. 1 in particular, the electrical switch structure includes a high-pressure tank 1 in which the arc extinguishing gas such as SF6 is stored at relatively high pressure, a low-pressure tank 2 which receives the pressurized gas after it has been used to blast the switch contacts, a housing 4 made of insulating material supported within the low-pressure tank and which contains the switch contacts, and a blast valve structure 3 located mainly within V the high-pressure tank I and which is adapted to establish a communication between the interior of tank I and the switch contact housing 4.

The switch contact structure within the housing 4 is seen to be of the double switching point type i.e. two sets of contacts are arranged electrically in series. The two sets of contacts are established by a double-ended stationary solid contact member 5, the opposite rounded ends 5a of which are arranged to engage the nozzle ends of two axially movable tubular contact members 6, 6' which include piston portions 6a slidable within sleeves 60. Pressure from the entering gas which flows through the open blast valve 3 applied against the piston portions 6a serves to actuate the nozzle ends of the contact members 6, 6 away from the rounded ends 5a of the stationary contact member and thus break the circuit at two points in series, the arcs drawn upon separation of the contacts being blasted by the pressurized gas and passed through the hollow interiors of the tubular contact members 6 and 6 into the low-pressure tank 2, by way of interposed filters, not illustrated, which serve to repurify the gas by removing the contaminants resulting from contact with the arc. The purified gas is then ultimately repressurized and returned to the highpressure tank.

After the are drawn between the contacts has been extinguished, the blast valve 3 is reclosed after a certain delay, and, as a result, the hollow contact members 6, 6' move back into contact with the ends of the stationary contact member 5 under the restoring counteraction of the biasing springs 6b which work against the back faces of the piston portions 6a. The delay in reclosing the contacts is made long enough to permit an isolating switch, not illustrated, which is connected in series with the switching points 5-6, 5-6 to be opened, thus isolating the line from the power interrupting switch structure.

As can readily be seen from FIG. 2, the blast valve structure 3 includes a cylindrical housing 7 which extends through opposite walls of the high-pressure tank structure 1 and is properly sealed at the wall pass-through points in order to avoid gas leakage. That portion of the wall of housing 7 located within the tank 1 is provided with a plurality of openings or ports 7a distributed over its circumference and through which the gas at high pressure can flow from the tank I into the housing structure 7. Located within the cylindrical housing 7 is a sleeve member 8 whose exterior diameter is approximately the same as the internal diameter of the housing part 7 so that the latter can act in the nature of a cylinder for guided longitudinal movement of the sleeve 8. Sleeve 8 is also provided with a plurality circumferentially spaced wall openings or ports which are so located as to register with the openings 70 in housing 7 when sleeve 8 occupies its lower position as depicted in FIG. 2. Sleeve 8, in turn, functions as a cylinder for guided movement of a valve sleeve 9 which has the function of covering and uncovering the ports 8a depending upon its position. In the lower position depicted in FIG. 2, the valve sleeve 9 covers the ports 8a so as to block off any flow of the pressurized gas from the tank 1 into and through the valve structure for entry into the low pressure tank 2. In the raised position of valve sleeve 9, as depicted in FIG. 3, the ports 8a are uncovered, thus permitting gas flow through the valve structure 3 into the low pressure casing for actuation of the switch contacts.

A hollow valve stem 9a is secured to, and extends upwardly from a transverse wall 9c within the sleeve 9 and the stem is guided by passage through a central opening within a circular plate 11 located within and fitted to the upper portion of sleeve 8. The valve stem 9a extends through a top closure cap 15 for the valve housing 7 where means, to be later described, are provided for actuating the valve stem 9a and hence the valve sleeve 9.

Fitted within the hollow valve stem 9a is a spindle 12 the lower portion of which extends through a central opening in the transverse wall 90 and is reduced in diameter to form a shouldered portion which establishes a seat for fixing the position of a circular gasket structure 14 adjacent the bottom face of wall 9c and which is secured on the spindle by means of a washer 12b and nut 12c which is screwed onto the lower threaded end 12a of the spindle. The gasket structure 14 is adapted to cooperate with a circular valve seat 8b located interiorly of sleeve 8 in order to permit one to close off the entrance passageway from the blast valve structure into the low pressure casing 2. The lower, threaded end 12a of the spindle 12 is also adapted to be screwed downwardly into a threaded central opening 130 in a spider plate 13 secured transversely within the lower portion of sleeve 8, also for a purpose to be later explained. The openings in the spider structure serve to permit free flow of the pressurized gas therethrough on its way to the low pressure tank 2.

Normal operation of the blast valve structure 3 to actuate the switch contacts 5a-6 and 5a6' entails an upward movement of the valve stem 9a and the inner spindle 12 as a unit. This is effected by means of a bolt and lever mechanism, not illustrated, which includes a part that passes through transverse openings 9b in the wall of valve stem 9 and a correspondingly positioned transverse bore in the upper part of spindle 12. As the spindle l2 and sleeve 9 are moved upwardly as a unit to the position shown in FIG. 3, it will be seen that, as previously explained, valve ports 8a will be uncovered as the valve sleeve 9 rises thus permitting flow of the pressurized gas from tank 1 through the valve housing 7 and spider plate 13 into the low-pressure tank 2. As valve sleeve 9 rises, it compresses a restoring spring 9d which serves to bias the valve sleeve 9 to its lower, valve port closing position.

When it is desired to service the blast 3 valve it is essential to the invention that the structure be designed in such manner as to permit disassembly of the valve components without opening the interior of either the highor low-pressure tanks 1, 2 to atmosphere. In accordance with the invention, it will be seen from FIG. 2 that the upper end of sleeve 8 is adapted to cooperate with a ring nut which operates within an upper internally threaded portion 7b of the cylindrical valve housing 7 so that after cap plate has been removed to gain access to the valve interior, sleeve 8 and the valve sleeve 9 are caused to raise by rotating nut 10 from the position depicted in FIG. 2 to that depicted in FIG. 4 whereby further upward movement is prevented by contact between the upper end face of nut 10 and an interiorly located snapring 16 which is set into a circular recess in the interior wall of housing 7. The upward movement of the parts 8 and 9 follows movement of upward movement of nut 10 due to the upward force exerted by the gas pressure in tank 2 which exceeds atmosphere pressure In this position, it will be seen that a lower cylindrical end portion 8d of sleeve 8 which is imperforat'e functions to close off all of the gas entry ports 7a, thus effectively closing off all possibility of gas flow out of the high-pressure tank 1. After this phase has been accomplished, spindle 12 is lowered and then rotated so that the lower end 1211 is screwed into the opening 130 in the stationary spider 13 thus drawing spindle l2 and the gasket structure 14 secured thereto downward until the lower face of the gasket comes firmly into contact with valve seat 811, this being the position depicted in FIG. 4 so that the entrance passage into the low-pressure tank 2 at the valve structure also becomes effectively sealed off. A screwplug 11a in plate 11 is now removed to vent the interior of the valve structure, and after venting, a snapring 17 set into a circular groove in the inner surface of sleeve 8 which normally retains the plate 11 against upward displacement is also removed, thus freeing the valve parts 9, 9a and 11 for removal through the upper open end of the valve housing 7. FIG. 5 shows the valve in its dismantled state, the sleeve 8 serving to block off gas discharge from the high-pressure gas tank 1, and the gasket 14 serving to close off the interior of the low-pressure gas tank 2 from atmosphere.

FIG. 6 illustrates a modified embodiment wherein the blast valve housing 20 and the closing element 21 are so designed that both the high-pressure and low-pressure sides are closed automatically by the closing element 21 during disassembly of the valve structure. The movable valve element 22 which serves to control flow of the high-pressure gas from the tank 1 into the low-pressure tank 2 is constructed as a tubular part with a ring-shaped inner piston portion 22a which is driven pneumatically by way of a control line 23 leading thereto. When piston 22a is admitted with pressure on its underside, the valve member 22 assumes the open position, represented by dashed lines, and the high-pressure gas flows over the path indicated by the flow arrows. A part 24 inserted into the lower end of valve member 22 serves both as a carrier for an annular sealing gasket 31 and as a guide for the valve element 22 and bears against a bottom part 21a of the valve housing part 21. The part 24 is secured against upward displacement relative to part 21 by means of a snapring 32 adapted to be engaged by a retaining ring 33 which is applied to the upper face of the annular gasket 31. The part 25 located within valve member 22 is rigidly connected with part 24 and serves likewise as a tight, sliding guide for the movable valve element 22. Longitudinal and transverse ducts in the parts 24, 25 ensure communication of the chamber above piston 22a with the low-pressure side. The opening of the valve element 22 is effected by exerting pneumatic pressure on the control line 23, while when pressure is removed, a biasing spring 26 which bears against the upper end wall of the valve element 22 effects closing of the valve. In order to permit disassembly of the valve structure, a screw 27 in the cover plate 29 is turned upwardly. The closing element 21 follows automatically into the locking position in a manner similar to that in which the valve corresponding to FIGS. 2 to 5 functions. After evacuation of the valve interior by removal of a screwplug 28 in end plate 30, the plates 29 and 30 can be safely removed thus providing access to the active parts of the valve which can then be removed for inspection and seal renewals.

Iclaim:

L In an electrical switch of the gas blast type, the combination comprising a high-pressure tank for storing gas such as SF6 at high pressure, a low-pressure tank, means providing a switch contact housing in said low-pressure tank, at least one set of switch contacts located within said housing and which are adapted to be blasted by gas at high pressure flowing from said high-pressure tank when said contacts are opened, said gas thereafter flowing from said switch contact housing into said low-pressure tank, and a blast valve for controlling flow of gas from said high-pressure tank into said switch contact housing, said blast valve including a cylindrical housing located partly within said high-pressure tank and provided with gas inlet ports through the wall thereof, the upper end of said housing projecting through the wall of said high-pressure tank and the lower end of said housing being in communication with said switch contact housing, a cylindrical sleeve slidably mounted within said valve housing, said sleeve including gas inlet ports through the wall thereof and being movable between a first position in which its inlet ports register with the inlet ports in said valve housing and a second position in which its inlet ports: are out of registry with the inlet ports in said valve housing, means including a movable valve member within said-sleeve for controlling flow of pressurized gas admitted into said sleeve through and out of sleeve and blast valve housing into said switch contact chamber when said sleeve occupies said first position, means for blocking off communication between said switch contact chamber and the interior of said sleeve and valve member when said sleeve occupies said second position, and means for releasing said valve member for removal through the upper part of said valve housing when said sleeve occupies said second position.

2. In an electrical switch of the gas blast type the combination comprising a high-pressure tank' for storing gas such as SF6 at high pressure, a low-pressure tank, means providing a switch contact housing in said low-pressure tank, at least one set of switch contacts located within said housing and which are adapted to be blasted by gas at high pressure flowing from said high-pressure tank when said contacts are opened, said gas thereafter flowing from said switch contact housing into said low-pressure tank, and a blast valve for controlling flow of said gas from said high-pressure tank into said switch contact housing, said blast valve including a cylindrical housing located partly within said high-pressure tank and provided with gas inlet ports through the wall thereof, the upper end of said housing projecting through the wall of said high-pressure tank and the lower end of said housing being in communication withsaid switch contact housing, a first cylindrical sleeve slidably mounted within said valve housing, said first sleeve including gas inlet ports through the wall thereof and being movable between a first position in which its inlet ports register with the inlet ports in said valve housing and a second position in which its inlet ports are out of registry with the inlet ports in said valve housing, a second cylindrical valve sleeve slidably mounted within said first sleeve, said second sleeve being movable from a first position in which it covers the inlet ports in said first sleeve to a second position in which the inlet ports in said first sleeve are uncovered, a tubular valve stem secured to said valve sleeve and extending through the upper end of said valve housing, a spindle located within said valve stem, the lower end of said spindle being provided with a gasketed valve plate adapted to cooperate with a valve seat provided at the interior of said first sleeve, said valve stem and said spindle being movable with said valve sleeve to the second position of said valve sleeve thereby to admit gas from said high-pressure tank through said inlet ports in said housing and first sleeve when said first sleeve is in its first position into the interior of said first sleeve and through the valve seat therein into said switch contact housing, means securing said spindle and gasketed valve plate thereon in a lower position in contact with said valve seat on said first sleeve when said first sleeve is in its second position thereby to close off communication to said switch contact housing through said first sleeve,

and means for releasing said valve sleeve and valve stem for removal through the upper end of said valve housing.

3. An electrical switch structure as defined in claim 2 and which further includes a ring nut threaded to the interior of said valve housing for movement along the axis of said valve housing, said ring nut being in contact with the upper end of said first sleeve and retaining the latter in its first position against the pressure of the gas in said switch contact housing.

4. An electrical switch structure as defined in claim 2 wherein said means securing said spindle and gasketed plate in its lower position in contact with said valve seat on said first sleeve is constituted by threaded engagement between the lower end of said spindle and a central threaded opening in a spider plate secured within said first sleeve below said valve seat.

5. In an electrical switch of the gas blast type, the combination comprising a high-pressure tank for storing gas such as SF6. at high pressure, a low-pressure tank, means providing a switch contact housing in said low-pressure tank, at least one set'of switch contacts located within said housintg and which are adapted to be blasted by gas at high pressure owing from said high-pressure tank when said contacts are opened, said gas thereafter flowing from said switch contact housing into said low-pressure tank, and a blast valve for controlling flow of gas from said high-pressure tank into said switch contact housing, said blast valve including a cylindrical housing located partly within said high-pressure tank and provided with gas inlet ports through the wall thereof, the upper end of said housing projecting through the wall of said high-pressure tank and the lower end of said housing being in communication with said switch contact housing, a cylindrical sleeve slidably mounted within said valve housing, said sleeve including gas inlet ports through the wall thereof and being movable between a first position in which its inlet ports register with the inlet ports in said valve housing and a second position in which its inlet ports are out of registry with the inlet ports in said valve housing, said sleeve further including gas outlet ports through the wall thereof adapted to register with gas outlet passages in the wall of said valve housing leading into said switch contact housing when said sleeve occupies said first position and being out of registry with said gas outlet passages when said sleeve occupies said second position, valve means including a movable valve member and valve seat located within said sleeve intermediate said gas inlet and outlet ports for controlling flow of pressurized gas through said sleeve, and means for releasing said valve means for removal through the upper end of said valve housing.

6. An electrical switch structure as defined in claim 5 wherein said sleeve member is constituted as a piston always subjected to the gas pressure within said switch contact chamber tending to move said sleeve from its first to its second position, and means for applying a releasable counter force for maintaining said sleeve in its first position. 

1. In an electrical switch of the gas blast type, the combination comprising a high-pressure tank for storing gas such as SF6 at high pressure, a low-pressure tank, means providing a switch contact housing in said low-pressure tank, at least one set of switch contacts located within said housing and which are adapted to be blasted by gas at high pressure flowing from said high-pressure tank when said contacts are opened, said gas thereafter flowing from said switch contact housing into said low-pressure tank, and a blast valve for controlling flow of gas from said high-pressure tank into said switch contact housing, said blast valve including a cylindrical housing located partly within said high-pressure tank and provided with gas inlet ports through the wall thereof, the upper end of said housing projecting through the wall of said high-pressure tank and the lower end of said housing being in communication with said switch contact housing, a cylindrical sleeve slidably mounted within said valve housing, said sleeve including gas inlet ports through the wall thereof and being movable between a first position in which its inlet ports register with the inlet ports in said valve housing and a second position in which its inlet ports are out of registry with the inlet ports in said valve housing, means including a movable valve member within said sleeve for controlling flow of pressurized gas admitted into said sleeve through and out of sleeve and blast valve housing into said switch contact chamber when said sleeve occupies said first position, means for blocking off communication between said switch contact chamber and the interior of said sleeve and valve member when said sleeve occupies said second position, and means for releasing said valve member for removal through the upper part of said valve housing when said sleeve occupies said second position.
 2. In an electrical switch of the gas blast type the combination comprising a high-pressure tank for storing gas such as SF6 at high pressure, a low-pressure tank, means providing a switch contact housing in said low-pressure tank, at least one set of switch contacts located within said housing and which are adapted to be blasted by gas at high prEssure flowing from said high-pressure tank when said contacts are opened, said gas thereafter flowing from said switch contact housing into said low-pressure tank, and a blast valve for controlling flow of said gas from said high-pressure tank into said switch contact housing, said blast valve including a cylindrical housing located partly within said high-pressure tank and provided with gas inlet ports through the wall thereof, the upper end of said housing projecting through the wall of said high-pressure tank and the lower end of said housing being in communication with said switch contact housing, a first cylindrical sleeve slidably mounted within said valve housing, said first sleeve including gas inlet ports through the wall thereof and being movable between a first position in which its inlet ports register with the inlet ports in said valve housing and a second position in which its inlet ports are out of registry with the inlet ports in said valve housing, a second cylindrical valve sleeve slidably mounted within said first sleeve, said second sleeve being movable from a first position in which it covers the inlet ports in said first sleeve to a second position in which the inlet ports in said first sleeve are uncovered, a tubular valve stem secured to said valve sleeve and extending through the upper end of said valve housing, a spindle located within said valve stem, the lower end of said spindle being provided with a gasketed valve plate adapted to cooperate with a valve seat provided at the interior of said first sleeve, said valve stem and said spindle being movable with said valve sleeve to the second position of said valve sleeve thereby to admit gas from said high-pressure tank through said inlet ports in said housing and first sleeve when said first sleeve is in its first position into the interior of said first sleeve and through the valve seat therein into said switch contact housing, means securing said spindle and gasketed valve plate thereon in a lower position in contact with said valve seat on said first sleeve when said first sleeve is in its second position thereby to close off communication to said switch contact housing through said first sleeve, and means for releasing said valve sleeve and valve stem for removal through the upper end of said valve housing.
 3. An electrical switch structure as defined in claim 2 and which further includes a ring nut threaded to the interior of said valve housing for movement along the axis of said valve housing, said ring nut being in contact with the upper end of said first sleeve and retaining the latter in its first position against the pressure of the gas in said switch contact housing.
 4. An electrical switch structure as defined in claim 2 wherein said means securing said spindle and gasketed plate in its lower position in contact with said valve seat on said first sleeve is constituted by threaded engagement between the lower end of said spindle and a central threaded opening in a spider plate secured within said first sleeve below said valve seat.
 5. In an electrical switch of the gas blast type, the combination comprising a high-pressure tank for storing gas such as SF6 at high pressure, a low-pressure tank, means providing a switch contact housing in said low-pressure tank, at least one set of switch contacts located within said housing and which are adapted to be blasted by gas at high pressure flowing from said high-pressure tank when said contacts are opened, said gas thereafter flowing from said switch contact housing into said low-pressure tank, and a blast valve for controlling flow of gas from said high-pressure tank into said switch contact housing, said blast valve including a cylindrical housing located partly within said high-pressure tank and provided with gas inlet ports through the wall thereof, the upper end of said housing projecting through the wall of said high-pressure tank and the lower end of said housing being in communication with said switch contact housing, a cylindRical sleeve slidably mounted within said valve housing, said sleeve including gas inlet ports through the wall thereof and being movable between a first position in which its inlet ports register with the inlet ports in said valve housing and a second position in which its inlet ports are out of registry with the inlet ports in said valve housing, said sleeve further including gas outlet ports through the wall thereof adapted to register with gas outlet passages in the wall of said valve housing leading into said switch contact housing when said sleeve occupies said first position and being out of registry with said gas outlet passages when said sleeve occupies said second position, valve means including a movable valve member and valve seat located within said sleeve intermediate said gas inlet and outlet ports for controlling flow of pressurized gas through said sleeve, and means for releasing said valve means for removal through the upper end of said valve housing.
 6. An electrical switch structure as defined in claim 5 wherein said sleeve member is constituted as a piston always subjected to the gas pressure within said switch contact chamber tending to move said sleeve from its first to its second position, and means for applying a releasable counter force for maintaining said sleeve in its first position. 